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A or B manually selects the respective controller when the Trim Air switch is ON.
An attempt to restore pack operation may be made by pressing the Pack Reset
switch.
If the pack cannot be reset, placing the respective Pack Control Selector to OFF
extinguishes the pack system fault light for use by the operating packs.
If both pack controllers A and B fail, air conditioning packs continue to operate
and the pack overheat protection system continues to operate normally. A pack
overheat results in a shut down.
Air Distribution
Recirculation Fans
Recirculation fans assist the packs to maintain a constant ventilation rate through
the cabin. The fans draw cabin air through filters, then reintroduce the air into the
conditioned air distribution system. Two fans are located above the main
passenger compartments and two fans are located below the main passenger cabin
floor. If a fan overheat is detected, electrical power is removed.
The number of recirculation fans operating is configured by:
• phase of flight,
• the number of operating air conditioning packs, and
• pack flow rates
On the ground, during climb, and during descent, two of the four recirculation fans
operate. During cruise, all four of the recirculation fans operate.
Lavatory and GalleyVentilation
Two ventilation fans, a primary and a backup, draw air from the galleys and
lavatories. The fans operate automatically. If the primary fan fails, the backup fan
automatically operates.
Conditioned air is provided to the galleys from the air distribution system.
Temperature Control
Hot trim air from the bleed air system added to the pack conditioned air controls
the temperature in each zone.
April 01, 2001
747 Operations Manual
Air Systems -
Air Conditioning System
Description
Copyright © The Boeing Company. See title page for details.
D6-30151-425 2.20.3
The zone temperature controllers regulate the temperature by controlling the
addition of hot trim air to the zone supply ducts through the trim air valves.
Zone Target Temperatures
The Passenger Temperature selector sets the master passenger cabin temperature
to between 65°F (18°C) and 85°F (29°C).
The target temperatures of each passenger zone may be modified plus or minus
10°F (6°C) within the range of 65°F (18°C) to 85°F (29°C) from the comfort
corrected master temperature. This is accomplished with the cabin temperature
panel located at door two right.
The temperature zone requiring the coolest temperature controls pack outlet
temperature.
Temperature Control With Loss of Trim Air System -
Passenger Backup Temperature Control
If trim air is not available to the distribution system, a backup mode activates. Pack
outlet temperature is regulated to achieve an average temperature between 65°F
(18°C) and 85°F (29°C), as set by the Passenger Temperature selector. If the
passenger temperature selector setting is unavailable to the pack temperature
controller, pack outlet temperature is regulated to achieve either the last passenger
temperature set or an average cabin temperature of 75°F (24°C).
Trim air is not available if master trim air switch is OFF, the EICAS alert message
TEMP ZONE message is displayed, or the center section of the bleed duct is
isolated.
Temperature Control Non-Normal Operations
If a system fault or overheat occurs in the flight deck or a passenger zone, the
master trim air valve closes and a backup mode is activated. An attempt to restore
zone temperature control can be made by pressing the zone temperature controller
reset switch.
Cargo Heat
When the equipment cooling system inboard exhaust valve is open, the heated air
exhausted from the electrical and electronic (E & E) compartment heats the
forward cargo compartment.
Aft cargo heat is provided by bleed air from the center section of the bleed air duct.
A thermal switch in the compartment opens and closes the temperature control
valve. When the compartment is cool, the thermal switch opens the valve. When
the compartment warms, the thermal switch closes the valve.
An overheat thermal switch provides overheat protection by opening and closing
an overheat/shutoff valve at higher temperatures.
April 01, 2001
747 Operations Manual
Copyright © The Boeing Company. See title page for details.
2.20.4 D6-30151-425
Air Systems -
Air Conditioning System
Description
Aft cargo heat is normally off until after engine start to increase bleed air available
for engine start. With the switch off, the electrically operated aft cargo heat valves
　
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